Nice point. Actually VS 2017 was in Consolas and Notepad++ in Courier New.
However, if I set Notepad++ to Segoe UI Emoji I can see all the characters (I had not checked that previously).
What happens with VS 2017 is that all characters are seen in every font.

Although Segoe UI Emoji is not a great font for programming, is better than nothing and I don’t need to deal with emojis every day.

Sites like fileformat.info will often give font lists for a given emoji. For example, U+1F431 CAT FACE’s page links to a fontsupport page for that character – and it doesn’t list Consolas, so I’m not sure whether that page is just out of date, or whether Consolas doesn’t include it, and VS 2017 is using some fallback mechanism.

As discussed a few months back, Windows has a font-fallback mechanism for its builtin apps (like notepad.exe) and I know MS Word and similar also will automatically change the font if you try a glyph not available in the current font (actually, with Word, it sometimes changes the font even when the glyph is available, from what I remember). Given that Visual Studio is also a Microsoft product, there’s a reasonable possibility* that they “cheat”, and use the fallback fonts when the default font you have in VS doesn’t include a glyph for a given character/emoji.

Notepad behaves like Notepad++, only shows the omitted characters on the Segoe UI Emoji font. However, VS 2017 definitely cheats. It always shows all characters for any font I select. However, the font really changes, only the special characters appear to be always the same. Having all characters available is useful for programming, I should say